Electrical means to normalize ablational energy transmission to a luminal tissue surface of varying size

ABSTRACT

Methods and devices for measuring the size of a body lumen and a method for ablating tissue that uses the measurement to normalize delivery of ablational energy from an expandable operative element to a luminal target of varying circumference are provided. The method includes inserting into the lumen an expandable operative element having circuitry with resistivity or inductance that varies with circumference of the operative element, varying the expansion of the operative element with an expansion medium, measuring the resistivity of the circuitry, and relating the resistivity or inductance to a value for the circumference of the operative element. In some embodiments the sizing circuit includes a conductive elastomer wrapped around the operative element. Other embodiments apply to operative elements that include an overlapping energy delivery element support in which the overlap varies inversely with respect to the state of expansion, and electrodes that sense the amount of the overlap.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/299,535, filed Jun. 9, 2014, entitled, “ELECTRICAL MEANS TO NORMALIZEABLATIONAL ENERGY TRANSMISSION TO A LUMINAL TISSUE SURFACE OF VARYINGSIZE,” which is a continuation of U.S. patent application Ser. No.12/143,404, filed Jun. 20, 2008, now U.S. Pat. No. 8,784,338, entitled,“ELECTRICAL MEANS TO NORMALIZE ABLATIONAL ENERGY TRANSMISSION TO ALUMINAL TISSUE SURFACE OF VARYING SIZE,” which claims priority to U.S.provisional patent application No. 60/936,865, entitled “ELECTRICALMEANS TO ESTIMATE DIAMETER MEASUREMENTS AND AN UNFURLING ELECTRODECONCEPT TO ADAPT TO ANY BODY ORIFICE,” filed on Jun. 22, 2007, each ofwhich are incorporated by reference in their entirety for all purposes.

INCORPORATION BY REFERENCE

All publications, patents and patent applications mentioned in thisspecification are herein incorporated by reference to the same extent asif each individual publication, patent or patent application wasspecifically and individually indicated to be incorporated by reference.

FIELD OF THE INVENTION

The present invention relates generally to medical methods and systemsfor treatment of body lumens. More particularly, the invention isdirected determining physiologic characteristics of body lumens such asthe esophagus in preparation for medical treatment such as ablationaltherapy.

BACKGROUND OF THE INVENTION

The human body has a number of internal body lumens, as in thegastrointestinal tract, with an inner lining or layer that can besusceptible to disease. As an example, gastroesophageal reflux disease(GERD), which involves inappropriate relaxation of the lower esophagealsphincter, manifests with symptoms of heartburn and regurgitation ofgastric and intestinal contents. Patients with severe forms ofgastroesophageal reflux disease can sometimes develop secondary damageof the esophagus due to the interaction of gastric or intestinalcontents with esophageal cells not designed to experience suchinteraction.

The esophagus is composed of three primary tissue layers; a superficialmucosal layer lined by squamous epithelial cells, a middle submucosallayer and a deeper muscle layer. When gastroesophageal reflux occurs,the superfacial squamous epithelial cells are exposed to gastric acid,along with intestinal bile acids and enzymes. This exposure may betolerated, but in some cases can lead to a condition known's asBarrett's esophagus, in which damage and alteration of the squamouscells causes them to change into taller, specialized columnar epithelialcells. Barrett's esophagus has important clinical consequences, as thecolumnar cells can become dysplastic, and then further progress toadenocarcinoma of the esophagus.

Accordingly, attention has been focused on identifying and removing thisabnormal Barrett's columnar epithelium in order to mitigate more severeimplications for the patient. Devices and methods for treating abnormalbody tissue by application of various forms of energy to such tissuehave been described, such as radio frequency ablation. However, precisecontrol of the depth of penetration of the energy means, these methodsand devices is critical to the success of such ablational therapy.Uncontrolled energy application can penetrate too deeply into theesophageal wall, beyond the mucosa and submucosal layers, into themuscularis externa, potentially causing esophageal perforation,stricture or bleeding. Among the factors and information needed foradministration of the correct amount of treatment energy to the tissueis knowledge of the size of the esophagus and area to be treated.

Medical procedures for treating Barrett's esophagus typically involvedeployment of an expandable catheter inside the esophagus. Expandablecatheters are preferred because the profile of the catheter is ideallyas small as possible to allow for ease of delivery, while treatment ofthe esophagus is most efficiently performed when the catheter is at orslightly larger than the diameter of the esophageal wall. Proper sizingand/or pressurization of the delivery device is desirable to preventover-distension of the organ, which can result in harm to the organ, orunder-expansion of the catheter, which can results in incompletetreatment. Accordingly, accurate and simple measurement of the size ofthe lumen and control of the pressure of the catheter on the lumensurface promotes the proper engagement and delivery of energy to theluminal wall so that a uniform and controlled depth of treatment can beadministered.

Ablational devices typically need to make an appropriate andreproducible therapeutic contact between an ablational surface and thesurface of a tissue area targeted for ablation. A number of ablationaldevices and methods for using them have been described in US Patents andApplications (U.S. Pat. No. 6,551,310 of Ganz issued on Apr. 22, 2003,application Ser. No. 10/370,645 of Ganz published as US2003/0158550 onAug. 21, 2003, application Ser. No. 10/426,923 of Stern published asUS2004/0087936 on May 6, 2004, application Ser. No. 10/754,452 ofJackson published as US2004/0215235 on Oct. 28, 2004, application Ser.No. 10/754,445 of Ganz published as US2004/0215296 on Oct. 28, 2004,application Ser. No. 11/244,385 of Jackson published as US2006/0095032on May 4, 2006, and application Ser. No. 11/633,938 of Jackson publishedas US2007/0100333 on May 3, 2007) that make use of an expandable balloonto exert pressure from behind the ablational surface to press it againstthe target tissue area. Inasmuch as the inner diameter of luminalorgans, such as gastrointestinal organs, vary in size, the extent orvolume to which a balloon is inflated to achieve therapeutic contactwill vary accordingly.

One currently available approach to creating consistency in the pressurethat supports an appropriate or desirable level of therapeutic contactis to pre-test the target ablation site in order to know what inflatedair volume is appropriate. Accordingly, measurements may be taken whilepressurizing an oversized balloon to a specific pressure (for example, 4psig) and then used to estimate the diameter of the esophagus, asdescribed in U.S. patent application Ser. No. 11/244,385 of Jackson,published as US 2006/0095032. While this technique works well underideal circumstances, in practical circumstances, leaks in the system cancause the production of inaccurate diameter estimates. Preventing leakshas been shown to be difficult as there are various locations in thesystem where a leak may occur.

Therefore, there is a need for alternative means of measuring thediameter or circumference of a body lumen in anticipation of atreatment, such as an ablation. This disclosure describes alternativedevices and methods of accomplishing this task.

SUMMARY OF THE INVENTION

The present invention comprises methods and systems for sizing a bodylumen, such as the esophagus. The sizing of a body lumen can provideinformation that is useful for determining values for various parametersof therapeutic treatments as exemplified by ablation treatment, such asnormalizing the energy density delivered from an ablating surface to atissue surface. Although the following description focuses on exemplaryembodiments configured for treatment of the esophagus, other embodimentsmay be used to treat any other suitable lumen in the body. Further,although ablational treatment is described as an exemplary therapeutictreatment, the invention may be applied to any form of therapeutictreatment in which it is beneficial to normalize the delivery oftreatment to the size of a lumen being treated. In particular, themethods and systems of the present invention may be used wheneveraccurate measurement of a body lumen or uniform delivery of energy isdesired to treat a controlled depth of tissue in a lumen or cavity ofthe body, especially where such body structures may vary in size.

Embodiments of the invention relate to methods of measuring the size ofa body lumen, as for example an inner circumference, devices formeasuring such a lumen, and methods for ablating targeted tissue in abody lumen that make use of the size measurement to control the deliveryof ablative energy. The inner circumference may be considered theparameter most directly measured by the method, as sensing elements arearranged linearly along a surface aligned with the circumference of thelumen, but such measurements may also be related directly to diameterand cross-sectional surface area of the lumen, as such values may bebeneficial in some applications. Further, by a calculation that includesa longitudinal measure of a portion of the lumen, values may becalculated for a luminal surface area, as may be treated, for example,by an ablational device. Still further, if treatment is being directedto a fractional portion of the circumference of a lumen, those surfacearea values can be calculated as well.

Measuring the size of a body lumen, as exemplified by a measure of theinner circumference of a body lumen includes expanding the size of anoperative element within the lumen, the operative element having sensingcircuitry with resistivity that varies according to the size of theoperative element, varying the sensing circuitry in accordance with theexpansion of the operative element, measuring the resistivity of thesensing circuitry, determining the size of the lumen based on themeasuring step. This summary will focus on resistivity as the exemplaryfeature of the circuitry that varies in accordance with the size of theoperative element of the lumen it occupies, but all that which is saidwith regard to resistivity may be applied to inductance as well.Embodiments that make use of inductance will, however, be brieflysummarized further below.

Varying the size of the operative element, for example by expanding it,may be performed by expanding an inflatable balloon within the operativeelement, and may include expanding the size of the operating element toexert a predetermined pressure on the lumen. The expansion medium may beeither a liquid or a gas. In some embodiments, the pressure is typicallybetween about 1 psig and about 7 psig; in some embodiments it is betweenabout 3 psig and about 5 psig, and in particular embodiments thepressure is about 4 psig. In some embodiments of the method, varying thedegree of expansion of the operative element includes automaticallyinflating and/or deflating a balloon. These pressures have beendetermined to be appropriate for effecting a coaptive ablation ofgastrointestinal luminal walls. In embodiments of the invention that aredirected toward other target sites or directed toward other types oftreatment with other objectives, other pressures may be beneficial andare included as embodiments of the method.

In some embodiments of the method, varying or expanding the size of theoperative element includes expanding the size of the operative elementto achieve a predetermined resistivity of the size-sensing circuitryincluded within the operative element. In some embodiments, thecircuitry includes size-sensing elements that include points ofelectrical contact. In other embodiments, the circuitry may includesize-sensing elements that have any one or more of brush elements,optical sensors, magnetic contact points, or electro-mechanical contactpoints.

In some embodiments of the method, varying the size-sensing circuitryincludes or causes stretching a conductive elastomer that is includedwithin the circuit, the conductive elastomer being wrapped around atleast a portion of the expandable operative element, the resistivity ofthe conductive elastomer increasing as it stretches in accordance withthe expansion of the size of the operative element.

In other embodiments of the method, expanding the operative elementincludes decreasing an area of overlap between two longitudinal edges ofa circumferentially-expandable energy delivery support having twolongitudinal edges that overlap each other, the amount of overlapbetween the two edges decreasing in accordance with the size of theoperative element expanding. In these embodiments, decreasing the areaof overlap between the two edges of the energy delivery support variesthe sensing circuitry, such circuitry being formed by sensing elementsthat arranged on both edges of the energy delivery support in the regionof overlap, the resistance of the formed circuitry varying in accordancewith the amount of the area of overlap.

Some embodiments of the method may include more than one approach tosizing the lumen by varying the sensing circuitry as have beensummarized. For example, some embodiments may make use both ofsize-sensing circuitry that includes a conductive elastomer as well ascircuitry that is responsive to changes in the amount of overlap of twoablational element delivery support edges.

Embodiments of the invention include devices for measuring the size of abody lumen, as for example the circumference of the body lumen asreflected in the circumference of an expandable operative element thatis expanded within the lumen. Such devices include an expandableoperative element having a circuitry whose resistivity (or inductance)varies according to the size, the circumference, for example, of theoperative element. Some embodiments of the device include an inflatableballoon that is substantially responsible for expanding the operativeelement, but other embodiments may include operative elements thatexpand by mechanical means that are equally capable of exerting pressureagainst a lumen.

In some embodiments of the device, the operative element furtherincludes one or more energy delivery elements, as for example,radiofrequency delivery elements to effect an ablation treatment ontarget tissue. These energy delivery elements may include aradiofrequency electrode, an array of electrodes, or solid-statecircuitry. In various embodiments, the ablative energy elements may bearranged directly on the expandable balloon, or arranged on an electrodesupport that is itself engaged around the balloon. In other embodiments,alternative forms of energy and appropriate delivery elements may beincluded, such as microwave energy emanating from an antenna, lightenergy emanating from photonic elements, thermal energy transmittedconductively from heated ablational structure surfaces or as conveyeddirectly to tissue by heated gas or liquid, or a heat-sink draw ofenergy, as provided by cryonic cooling of ablational structure surfaces,or as applied by direct cold gas or fluid contact with tissue.

In some embodiments of the device, the circuitry includes a portion of aband of conductive elastomer wrapped around a circumferentiallyexpandable portion of the operative element, such as around aninflatable balloon, such that when the balloon is contracted, the lengthof the conductive elastomer band is contracted, and when the balloon isexpanded, the length of the conductive elastomeric band is expanded. Inother embodiments, the device includes an ablational energy deliveryelement support arranged around the balloon, and the band of conductiveelastomer is wrapped around the support. The conductive elastomericportion of size sensing circuits of these embodiments is configured torelate size-sensing data by virtue of the electrical properties such asresistivity or inductance that vary according to the degree ofcontraction or stretch of the conductive elastomer.

Embodiments of circuitry that include a conductive elastomer within asize-sensing circuit thus depend on the particular construction of thedevice. For example, the conductive elastomer may be wrapped around anexpandable member included within the operative element, such as aninflatable balloon. In some embodiments, treatment delivery elementssuch as ablation energy delivery elements may be arranged directly onthe balloon, and in other embodiments, an intervening ablation energydelivery element support carrying the energy delivery elements may bewrapped around the balloon. In all these embodiments, a conductiveelastomer may be wrapped around any portion of the operative elementthat expands in a manner that accords with the circumferential expansionof the operative device as a whole. In still other embodiments, theconductive elastomer may be applied to an internal surface of theballoon, or the internal surface of any portion of the operative elementthat expands in a manner that accords with he circumferential expansionof the operative device as a whole.

In other embodiments of the device, as noted above, the device includesan ablational energy delivery element support arranged around aninflatable balloon. The support of these device embodiments has a firstedge and a second edge that mutually overlap each other, and the supportis circumferentially expandable by the balloon such that when theballoon is contracted an area of mutual overlap of the two edges isinversely related to the amount of expansion of the balloon. Forexample, when the balloon is contracted or not expanded, the area ofmutual overlap is relatively large, and when the balloon is expanded,the area of mutual overlap of the two edges is relatively small. Inthese embodiments, the circuitry includes size sensing elements on bothedges of the overlapping support; such elements are configured to makean electrical connection across the area of mutual overlap to form acircuit with a particular resistivity, and the elements are alsoconfigured such that the particular circuit-forming electricalconnection between sensing elements varies according to the amount ofmutual overlap of the two edges.

In these device embodiments, configuration of the sensing elements andtheir pattern or distribution between the two longitudinal edges of anablational energy delivery support may take various forms; threeexemplary embodiments will be summarized. In some embodiments of thedevice, the first edge includes a single size-sensing element and thesecond edge includes a plurality of spaced-apart size-sensing elements,the particular element among the plurality of elements on the secondedge that makes a connection to the element on the first edge variesaccording the amount of mutual overlap of the two edges, and theresistivity of circuit thus formed varies according to which of theelements on the second edge is included in the circuit. In otherembodiments of the device, the first edge includes a single sensingelement and the second edge includes a plurality of closely-spacedsensing elements, the elements configured such that the element on thefirst edge can make a connection with one of the plurality of theelements on the second edge or with two adjacent elements, and theresistivity of circuit formed varies according to which one or which twoof the elements on the second edge are included in the circuit. In stillother embodiments of the device, the first edge includes a singlesensing element and the second edge includes an elongated sensingelement; the elements are configured such that the single element on thefirst edge forms a circuit by making contact with the elongated elementon the second edge at a point that varies along its length, therebycreating a circuit of varying length, and the resistivity of the circuitvaries according to the length of the element on the second edge that isincluded in the circuit. All three of these approaches provide data fromthe size-sensing elements that relates to the size of the operativeelement in real time.

Embodiments of the invention further include methods for ablating targettissue in a body lumen. These methods basically include sizing steps ashave been summarized that are coupled with the delivery of ablationenergy at a level that is normalized per the sizing data provided by thesizing steps. The method includes inserting an expandable operativeelement into the lumen, the operative element having sensing circuitrywith resistivity that varies according to the size of the operativeelement, expanding the operative element to contact the target tissue ata predetermined pressure, varying the sensing circuitry in accordancewith the expansion of the operative element, measuring the resistivityof the sensing circuitry, determining the size of the lumen based on themeasuring step, and controlling the delivery of energy to the operativeelement according to the size of the lumen.

Controlling delivery of energy may manifest or be expressed in terms ofdelivery of energy to the operative element, or in terms of delivery ofenergy from the operative element to the tissue. Further, ablation maybe controlled in terms of energy, power, or power density as it isnormalized to target tissue surface area. Thus, embodiments of themethod make may use of an operative element that includes an expandableballoon for expanding the operative element, an ablational energydelivery surface for ablating tissue, and circuitry with a variableresistivity for measuring the circumference of the operative element.

In some embodiments of the method, controlling delivery of energyincludes delivering energy in proportion to the surface area of thetargeted tissue with which the operative element is in contact. Invarious embodiments of the method, controlling delivery of energyincludes controlling delivery of energy from the operative element intothe tissue, and more specifically, may include controlling the depth towhich tissue is ablated.

In various embodiments of the method, controlling delivery of energyincludes controlling an amount of power delivered to the tissue overtime, and more specifically may include normalizing power delivered tothe tissue over time. In various embodiments of the method, controllingdelivery of energy includes controlling an amount of energy delivered tothe tissue over time, and may include controlling delivered energydensity. In other embodiments of the method, controlling delivery ofenergy includes monitoring and controlling tissue impedance over time,or controlling delivery of energy includes monitoring and controllingtissue temperature over time.

In other embodiments of the method, controlling delivery of energy mayfurther include controlling an amount of power delivered to the tissueby rapidly increasing the power until it reaches a set target value; andin some embodiments it may include the amount of power delivered isperformed using a proportional integral derivative controller.

As mentioned above, embodiments of the methods and devices provided heremay make use of inductance in place of or in addition to resistivity asan electrical means by which to measure the size, the circumferentiallength for example, of an expandable operative element, and byinference, the circumference and related dimensions of a lumen in whichthe device has been place. Thus, for example, the method of measuringthe size of a body lumen may include expanding an operative elementwithin the lumen, the operative element having sensing circuitry withinductance that varies according to the size of the operative element,varying the sensing circuitry in accordance with the expansion of theoperative element, measuring the inductance of the sensing circuitry,and determining the size of the lumen based on the measuring step.

By way of another example of using inductance as a size-measuringparameter of sensing circuitry, a device for measuring the size of abody lumen may include an expandable operative element includingcircuitry whose inductance varies according to the size of the operativeelement. By way of a further example of implementing inductance as anapproach to sizing a body lumen in the context of an ablationaltreatment, a method for ablating targeted tissue in a body lumen mayinclude inserting an operative element into the lumen, the operativeelement having sensing circuitry with inductance that varies accordingto the size of the operative element, expanding the operative element tocontact the target tissue at a predetermined pressure, varying thesensing circuitry in accordance with the expansion of the operativeelement, measuring the inductance of the sensing circuitry, determiningthe size of the lumen based on the measuring step, and controlling thedelivery of energy to the operative element according to the size of thelumen.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A-1D provide perspective views of an ablation device with anoverlapping electrode support furled around an expandable balloon, theoperative element including a balloon and an electrode support in anexpanded state. FIG. 1A shows the support pulled away from the balloonto clarify that a portion of the support and an edge is adherent to theballoon, and another portion and its edge is not connected to theballoon.

FIG. 1B shows the operative element of the device with the non-adherentportion of the support furled around the balloon in a deployableconfiguration, the non-adherent portion and its edge overlapping aroundthe adherent portion.

FIG. 1C shows the device of FIGS. 1A and 1B with an optional feature ofthe operative element 140, one or more elastic bands 180 wrapped aroundthe electrode support 160.

FIG. 1D shows the device of FIG. 1C in a collapsed state, with balloonportion being uninflated (or deflated), this being the state of thedevice when it is being deployed into a lumen and being positioned at atarget site, as well as the state of the device after deliveringablation energy and about to be removed from the lumen.

FIGS. 2A and 2B provide views of an embodiment of a circumferentiallyoverlapping electrode support with a set of discrete measuringelectrical contacts linearly arranged in a circumferential orientationon the outer aspect of an inner-laying edge of the support and a singlecontacting electrode on the inner aspect of the outer-laying edge of thesupport, the contacts within the area of mutual overlap on theirrespective edge. FIG. 2A is a view of the support in acircumferentially-contracted state, with extensive overlap between theinner-laying and outer-laying edges of the support.

FIG. 2B is a view of the support in a circumferentially-expanded state,with a small amount of overlap between the edges of the support.

FIGS. 3A and 3B provide views of an embodiment of a circumferentiallyoverlapping electrode support with a set of closely-spaced measuringelectrical contacts linearly arranged in a circumferential orientationon the outer aspect of an inner-laying edge of the support and a singlecontacting electrode on the inner aspect of the outer-laying edge of thesupport, the contacts within the area of mutual overlap on theirrespective edge. FIG. 3A is a view of the support in acircumferentially-contracted state, with extensive overlap between theedges of the support.

FIG. 3B is a view of the support in a circumferentially-expanded state,with a small amount of overlap between the edges of the support.

FIGS. 4A and 4B provide views of an embodiment of a circumferentiallyoverlapping electrode support with a size-sensing circuit that includesa connection between an electrical contact on the inner aspect of anouter-laying edge and a site along the length of an electrode in theform of a conductive material linearly arranged in a circumferentialorientation on the outer aspect of the inner-laying edge of the support,the contact occurring within the area of mutual overlap. FIG. 4A is aview of the support in a circumferentially-contracted state, withextensive overlap between the edges of the support.

FIG. 4B is a view of the support in a circumferentially-expanded state,with a small amount of overlap between the edges of the support.

FIGS. 5A-5C show cross-sectional views of the deployable embodimentdepicted in FIG. 4B with the balloon at varying levels of expansion, andthey further depict an elastic band surrounding the furled support whichurges collapse of the balloon and the slidable return of the overlappingedges to their state of maximal overlap. FIG. 5A shows the balloon in acontracted state, with the support in a state of maximal overlap.

FIG. 5B shows a cross-sectional view of the balloon in a state ofpartial expansion, with the support in a state of partial overlap.

FIG. 5C shows a cross-sectional view of the balloon in a state of fullexpansion, with the support in a state of minimal overlap.

FIGS. 6A-6C provide schematic views of a band of conductive elastomer invarious states of collapse to expansion, as in the configurations thatwould correspond to the embodiments depicted in FIGS. 5A-5C, with anohmmeter measuring the resistivity at each state. FIG. 6A shows the bandof conductive elastomer in a state of minimal expansion, the ohmmeterdisplaying low resistivity.

FIG. 6B shows the band of conductive elastomer in a state of moderateexpansion, the ohmmeter displaying mid-level resistivity.

FIG. 6C shows the band of conductive elastomer in a state of fullexpansion, the ohmmeter displaying high resistivity.

FIG. 7 provides a flow diagram of a method for ablational treatment thatincludes normalizing ablational energy per unit surface area of targettissue.

DETAILED DESCRIPTION OF THE INVENTION

Principles and General Considerations

An object of this invention is to provide high-resolution measurementsof the size of a body lumen in real time, when an ablative operationalelement is positioned in the lumen. The measurement relates mostdirectly to the operative element itself, however, as the operativeelement fills the lumen upon its expansion, the measurement alsoreflects the size of the lumen. Body lumens are typically compliant andvariable in size according to their contents or moment-to-momentphysiological status, as lumens typically have no hard structural orimmediately constraining features such as bone. The sizing methodsprovided herein thus focus on the size of the lumen, as reflected by thesize of a space-filling operative element, in the moment as theoperative element resides in the lumen, which is typically immediatelyprior to delivery of a form of therapy, such as ablational energy, fromthe operative element to the inner surface of the lumen. The fundamentalparameter upon which these measurements are based includes resistivityof one or more size-sensing circuits, as the circuits are configured toprovide an informative signal that relates to the size of theoperational element filling the lumen. The size dimension being measuredcan relate to any of radius, diameter, or circumference, as all thesevalues are interrelated, however the signal typically relates mostdirectly to circumference. In addition to resistivity, other electricalparameters of the circuits that may be directed to this same objectinclude inductance.

Two basic approaches to the measurement are provided by methods anddevices provided herein. One approach relates to the use of a conductiveelastomer arranged around the circumference, or a portion of thecircumference of the expandable operative element. In this approach, asize-sensing circuit measures the resistivity of the operative elementas changes shape, for example, as it expands or stretches. A secondapproach to measurements of expandable operative elements relates to theuse of operative element embodiments that include slidably overlappingleaves as part of the mechanism by which they radially expand. These twoapproaches are described below, first in terms of the basic operatingprinciples, structures, and methods, and then later, in the context ofspecific illustrated examples. Still further, these embodiments aredescribed in the larger context of the use of these operative elementson ablation catheters.

In some embodiments of the invention, in accordance with the firstapproach noted above, an elastic element or elastomer iselectrically-conductive, as provided by the use, for example byinclusion of silver-filled silicone. The resistivity of anelectrically-conductive elastomer varies as a function of the extent towhich the elastomer is stretched; when electrically-conductive elastomeris stretched, it has relatively high resistivity, and when contracted ithas relatively low resistivity. Thus, by monitoring the resistivity ofan electrically-conductive elastomer wrapped around an expandingballoon, a measure of the size (as exemplified by the circumference) ofthe balloon is provided. The system may be empirically calibrated priorto use in a body lumen, by testing resistivity as a function of thedegree of expansion of the balloon, for example, when collapsed, andwhen at varying degrees of expansion to a state of the maximal expansionanticipated in normal use. Based on this information and other empiricalinformation, these resistivity values permit estimates of the balloondiameter.

Some alternative embodiments of the invention make use of strainmeasurements to estimate the size of body lumen, such as an esophagus,prior to performing an ablation treatment. Elastic members such as bandsmay be wrapped around the edges of an expansion balloon, attached to thesurface of the balloon such that when balloon is expanded, the elasticelements stretch to coincide with the expansion of the balloon. Thisballoon expansion forces the elastic member to elongate, which causes anincrease in axial load to the elastic element between the attachmentpoints of the elastic element-balloon interface, such load can bemeasured as strain which can in turn be related to size.

In alternative embodiments of the invention, instead of using aconductive elastomer, the elastic element may be attached to theoperative element (or a portion thereof whose expansion relates to theexpansion of the element as a whole) through an intermediary elementused for measuring forces or strain. For example, a strain gauge elementmay be attached directly to the balloon and to the end of the elasticelement. As the elastic element stretches it increases the strain on thestrain gauge, and such strain data can be used to provide sizeinformation, which can be used in turn, to normalize the delivery oftreatment to size parameters, such as luminal circumference or surfacearea.

In accordance with the second approach to device or lumen measurementsas noted above, some embodiments of the invention include features thatallow the operative element 140 to determine its own size, as its sizevaries by expanding and contracting within a body lumen, in preparationfor the delivery of ablational energy. More specifically, the expansionstate or size can be related to absolute dimensions of radius, diameter,or circumference. These values, derived from the operative element andassociated size-sensing circuitry, can be related to the real timedimensions of the lumen at the site where the operative element issituated. More particularly, these dimensions, in combination with alongitudinal measure of a portion of a lumen, can all be related to thesurface area of mutual contact between an ablational energy deliveryelement such as an array of radiofrequency electrodes and the targettissue. The object of knowing this surface area dimension is to enablethe delivery of a specific power density (Watts/cm²) or energy density(Joules/cm²) to the tissue area that is targeted for ablation. Incontrast to the pressure-based sizing balloon-based approach describedin U.S. patent application Ser. No. 11/244,385 of Jackson (US PatentPub. No. 2006/0095032), the approach described herein is based onresistivity or inductance of size-sensing circuits whose resistancevaries according to the amount of overlap of electrode support edges.

As shown generally in FIGS. 2A-4C, as the diameter of the expandableballoon expands, the overlapping region 190 of the two ends of theunfurling ablational energy delivery element (radiofrequency electrodesbeing an exemplary ablational energy delivery element) support 160decreases. Thus, the amount of surface area of the electrode supportexposed to the tissue is inversely proportional to the overlappingsurface of the electrode support. Described below in greater detail arevarious electrical approaches with which to estimate that overlappingsurface area, and thereby estimate the area of tissue exposed to theablational surface. Briefly, electrical contacts 170 are placed in theoverlapping region 190 on both sides of the electrode support 160 withinthe overlapping region. The electrical contacts are configured in such away that those that are able to form a complete circuit provideinformation that relates to the degree of overlap, and thus to thecircumference of the operative element at that point in time.

In some embodiments of the invention, the size-sensing electricalcontact points can be alternatively replaced with optical sensors,magnetics, or other electrical, electro-mechanical or optical means todetermine the amount of electrode overlap. The opposing outward force ofthe balloon inflating from pressure with the constraining inward forcefrom elastic members provides pressure that keeps the sensing elementsin contact. Multiple circuits may be included within the system toprovide redundancy, as for example to reduce the likelihood of thetissue or other material preventing physical contact between the twolayers, or to provide multiple signals that can be integrated to providehigher resolution measurement. As another approach to protecting frominterfering debris, the undersurface of the electrical contact pointscan include a metallic brush element to improve contact in the presenceof tissue or other debris.

In other embodiments of the invention, rather than using resistivefeedback, the inductive changes between the electrical circuit formedfrom contacts on the facing edges of the inner-laying and out-layingoverlapping edges of the electrode support may be monitored. Inductanceis a function of both the gap between the two circuits (it is desirableto keep as constant as possible) and the amount of overlap of theelectrode/circuit areas.

Methods of estimating the surface area of luminal tissue with whichelectrodes are in contact include using measurements of electricalresistance with respect to tissue, and include the application ofrelated Formulas 1 and 2, as described below.R=ρ(L/A)  Formula 1

-   -   ρ=resistivity=1/electrical conductivity of the circuit. (This is        an inherent function of electrode and wire compositions, and the        conductivity of the tissue, the latter being different for each        patient.)    -   L=length of the electrode    -   A=area of the electrode    -   R=resistance of electrode circuit

Therefore, based on the Formula 1, to develop a predictable correlationbetween the electrode resistance and contact area, the followinginformation is needed:Area in contact with tissue=ρ(L/R)  Formula 2

Thus, to determine area, measurements of p and R are needed. The pestimate is obtained by measuring resistivity of the tissue, and an Restimate is obtained by measuring the starting resistance of the exposedcircuit that is in contact with the tissue.

Typically, the manufacturing process by which embodiments of theinvention are made includes specifications that provide a match betweenresistivity of size-sensing circuits and circumference of the operativeelement, such that these relationships are known. Manufacturingprocesses may also include quality control steps such that therelationship between resistivity of sensing circuits and circumferenceof the operating element at various levels of expansion is validated. Inanother approach to providing assurance of the validity of circumferencemeasurements, an end-user can validate such measurements by checkingindividual operating elements with measurements of tubes of knowndimension. By any of these approaches, when practicing the inventivemethod described herein, the expansion of an operative element to apredetermined pressure will yield a given resistivity that can berelated to size of an operating element. According, in the practice ofthe method, it may be beneficial to use resistivity as a target value,and when using the operative element as a treatment device, the methodcan include expanding the operative element to achieve a given target orpredetermined resistivity.

Illustrative Examples and Embodiments

Turning now to illustrative examples of the approaches to measuring theinternal dimension of a body lumen, embodiments of operative elementsthat that include an electrode support 160 that wraps overlappinglyaround an expandable balloon 150 and which provides a base from whichsize-sensing elements operate will be described first; embodiments thatmake use of an electrically conductive elastomer as a measuring elementare described further below.

FIGS. 1A-1C provide perspective views of an ablation device 140 with anoperative element 140 that includes overlapping electrode support 160furled around an expandable balloon 150. An array of ablational energydelivery elements 165 such as radiofrequency electrodes is arranged onthe exterior surface of the electrode support. The operative element ismounted on the distal end of an ablation catheter, of which the distalportion of a shaft 142 is seen, and around which the balloon 150 isconfigured. FIG. 1A shows the electrode support 160 pulled away from theballoon 150 to clarify that a portion of the support and an inner edge162 is adherent to the balloon, and another portion and its outer edge164 is not connected to the balloon. FIG. 1B shows the non-adherentportion of the electrode support 160 furled around the balloon 150 in adeployable configuration, the non-adherent portion and its edgeoverlapping around the adherent portion. FIG. 1C shows an optionalfeature of the operative element 140, one or more elastic bands 180wrapped around the electrode support 160. In some embodiments, theelastic band 180 material is a conductive elastomer, as described ingreater detail below, which can be included in a size-sensing circuit toprovide information related to the degree of expansion of the operativeelement. FIG. 1D shows the device of FIG. 1C in a collapsed state, withballoon portion 150 being uninflated (or deflated), this being the stateof the device when it is being deployed into a lumen and beingpositioned at a target site, as well as the state of the device afterdelivering ablation energy and about to be removed from the lumen.

FIGS. 2A-6C focus on the overlapping electrode support 160, and thefeatures that allow determination of the state of expansion of thesupport; not seen in these particular views is an expandable balloon 150(see FIGS. 1A-1C) that resides internal to the support and whichprovides the expansive force. Thus, FIGS. 2A and 2B provide views of anembodiment of a circumferentially overlapping electrode support 160 witha set of discrete measuring electrical contacts 170 linearly arranged ina circumferential orientation on the outer aspect of an inner-layingedge 162 of the support 160 and a single contacting electrode 170 on theinner aspect of the outer-laying edge 164 of the support. The contactson both edges of the support lie within the area of mutual overlap 190on their respective edge. The number of sensing electrical contacts oninner-laying edge, in various embodiments, may vary typically betweenthree and ten, but may include any appropriate number suitable for thedimensions of the contacts and the support. FIG. 2A shows the support160 in a circumferentially-contracted state, with an extensive region ofoverlap 190 between the edges of the support. In this configuration, thecircuit that is completed by connection between the sensing electrode onthe outer-laying edge and the one sensing electrode of five possibleelectrodes is one that forms a circuit (bold line) with resistance R5.FIG. 2B shows the support 160 in a circumferentially-expanded state,with a small amount of overlap 180 between the edges of the support. Inthis configuration, the circuit that is completed by connection betweenthe sensing electrode on the outer-laying edge and the one sensingelectrode of five possible electrodes is one that forms a circuit (boldline) with resistance R2.

Another feature associated with the manner in which the inner-layingedge 162 and the outer-laying edge 164 of the energy-delivery support160 interact involves their ability to slide past each other withoutdisturbing the integrity or their generally flattened aspect; thisfeature derives from the stiffness of the material forming the support160, and its general non-self sticking nature. Embodiments of thesupport 160 typically comprise a flexible, non-distensible backing,formed from a thin, rectangular sheet of polymer materials such aspolyimide, polyester or other flexible thermoplastic or thermosettingpolymer film. The support 160 may also comprise polymer coveredmaterials, or other nonconductive materials. Additionally, the backingmay include an electrically insulating polymer, with anelectro-conductive material, such as copper, deposited onto a surface sothat an electrode pattern can be etched into the material to create anarray of electrodes. The slidability of the two longitudinal edgesacross each other is not particularly visible in FIGS. 1A-1C, however itis depicted in FIGS. 2A-5C. For example, the overlapping region 190 iscomparatively large in FIGS. 2A, 3A, and 4A, and comparatively small inFIGS. 2B, 3B, and 4C, the change having occurred by the inner 162 andouter 164 edges having slid past each other. The slidability is ofparticular note in FIGS. 5A-5C, as in this embodiment an elastic band180 surrounds the overlapping edges. The elastic band exerts acompressive force that urges the collapse of the operative element asthe balloon deflates, but the overall balance of compressive force andthe slidability of the overlapping edges is still one that allowsslidability to prevail in spite of the compression being exerted by theelastic band.

FIGS. 3A and 3B provide views of an embodiment of a circumferentiallyoverlapping electrode support 160 with a set of closely-spaced measuringelectrical contacts 170 linearly arranged in a circumferentialorientation on the outer aspect of an inner-laying edge 162 of thesupport and a single contacting electrode 170 on the inner aspect of theouter-laying edge 164 of the support 160, the contacts within the areaof mutual overlap 180 on their respective edge. FIG. 3A shows thesupport 160 in a circumferentially-contracted state, with extensiveoverlap between the two longitudinal edges of the support, while FIG. 3Bshows the support 160 in a circumferentially-expanded state, with asmall amount of overlap between the edges of the support. In FIG. 3A,the sensing electrode on the outer-laying edge is in contact with asingle sensing electrode on the inner-laying edge that completes acircuit with a resistance R6. In FIG. 3B, the sensing electrode on theouter-laying edge is in contact with two adjacent sensing electrodes onthe inner-laying edge which by themselves would form circuits withresistances of R1 and R2 respectively. In the circumstance, asillustrated, where the circuit formed includes both inner-laying sensingelectrodes yield a circuit with a resistance, as noted in the figure,where R=1/(1/R1+1/R2). The difference between the embodiments depictedin FIGS. 2(A and B) vs. those in 3(A and B) is that the latterembodiment yields greater resolution or granularity in thecircumferential measurement. Other dimensions of sensing electrodesbeing equal, the embodiment of FIG. 3 provides twice as many valuepoints than are provided by the embodiment of FIG. 2. Resolution ofmeasurements can also be generally understood as being a function of thenumber (or dimensions) of sensing electrodes distributed along theregion of overlap 190.

FIGS. 4A and 4B provide views of an embodiment of a circumferentiallyoverlapping electrode support 160 with a size-sensing circuit 175 thatincludes a connection between an electrical contact on the inner aspectof an outer-laying edge 164 and a site along the length of an elongatedsensing electrode 172 in the form of a conductive material linearlyarranged in a circumferential orientation on the outer aspect of theinner-laying edge 162 of the support, the contact occurring within thearea of mutual overlap 180. FIG. 4A shows the support 160 in acircumferentially-contracted state, with extensive overlap between theedges of the support, while FIG. 4B shows the support 160 in acircumferentially-expanded state, with a small amount of overlap betweenthe edges of the support. In this expanded configuration, the elongatedelectrode 172 can be seen to functionally-divided into two segments, aportion of the electrode 172 i is included within the circuit 175, and aportion of the electrode 172 o is outside of the circuit. This situationdiffers from that of the elongated electrode 172 in the contractedconfiguration of the electrode support 160 as seen in FIG. 4A, where thewhole of the electrode or where nearly the whole of the electrode isincluded within the circuit 175. Inasmuch as the resistivity of thecircuit is increased by the length of the electrode included in thesensing circuit, the resistivity Rvar of the circuit 175 formed in FIG.4A is relatively high, and the resistivity Rvar formed in FIG. 4B isrelatively low. From such differences in resistivity (or inductance, inalternative embodiments), the sensing circuitry provides data that areinformative with regard to the circumference of the support 160.

FIGS. 5A-5C show cross-sectional views of the deployable embodiment ofan operative element depicted in FIG. 4B with the balloon 150 at varyinglevels of expansion, and they further depict an elastic band 180surrounding the furled support 160 which urges collapse of the balloonand the slidable return of the overlapping edges to their state ofmaximal overlap. In some embodiments, this elastic band is formed from aconductive elastomer that can be included in a size-sensing circuit 175,as described below. FIG. 5A shows the balloon 150 in a contracted state,with the support in a state of maximal overlap. FIG. 5B shows across-sectional view of the balloon 150 in a state of partial expansion,with the support in a state of partial overlap. FIG. 5C shows across-sectional view of the balloon 150 in a state of full expansion,with the support in a state of minimal overlap.

Turning to some general considerations, FIGS. 2A-4B show embodiments inwhich the inner or center-facing aspect of the outer-laying edge 164 hasa single electrical contact that makes contact and complete size-sensingcircuits 175 with varying forms of electrodes on the outer-facing aspectof the inner laying edge 162 of overlapping edges of an electrodesupport 160. For the purposes of description it can be understood thatthe outer-laying edge 164 is a first edge of the support and that theinner-laying edge 162 is a second edge of the support. However, it canalso be understood that the labels of first and second are arbitrary,and that further, in alternative embodiments, the distribution ofelectrodes between inner- and outer-laying support edges may reversedsuch that the outer-laying edge 164 is a second edge of the support andhas multiple sensing electrodes, and the inner laying edge 162 is afirst edge with a single sensing electrode, such configuration having nosubstantive difference between the function and the information relatedto the size-sensing circuitry.

Turning now to illustrative examples of the approaches to measuring theinternal dimension of a body lumen, embodiments of operative elementsthat that include a piece of conductive elastomer wrapped around theoperative element will be described. FIGS. 6A-6C provide schematic viewsof a band of conductive elastomer 180 in various states ranging fromminimal circumference to full or nearly-full circumferential expansion(as in the configurations that would correspond to the embodimentsdepicted in FIGS. 5A-5C) with an ohmmeter measuring the resistivity asensing circuit 175 at each state of expansion. The conductiveelastomeric band 180 includes a non-conductive gap 180 a, the circuitryconnecting to the conductive band on either side of the non-conductivegap. The composition of embodiments of the conductive elastomer includesconductive elements distributed within a polymeric matrix. When thepolymeric matrix is in its preferred or fully contracted state, theabsolute spatial density of the conductive elements is maximal, andconsequently conductivity is maximal and resistivity is minimal. On theother hand, when the polymeric matrix is stretched, the spatial densityof the conductive elements is diminished, conductivity decreases, andresistivity increases.

A circuit that includes a conductive elastomer arranged around anoperative element in a manner such that the length of the elastomerreflects the degree of expansion of the circumference of the operativeelement thus provides a signal that can be related to the circumferenceof the operative element. FIG. 6A shows the band of conductive elastomer180 in a state of minimal expansion, the ohmmeter displaying lowresistivity. FIG. 6B shows the band of conductive elastomer 180 in astate of moderate expansion, the ohmmeter displaying mid-levelresistivity. FIG. 6C shows the band of conductive elastomer 180 in astate of full expansion, the ohmmeter displaying high resistivity.

Two bands of conductive elastomer are shown in the operative elementembodiment shown in FIG. 1C, one at either longitudinal end of theelectrode support 160. The cross-sectional views provided in FIGS. 5A-5Cand 6A-6C show a single band of conductive elastomer. Embodiments of theinvention thus include those provided with one or more conductiveelastomer bands. Further, the configuration of the conductive elastomerpieces may vary according to the practical needs of securing theelectrode support, or securing or supporting, or otherwise constrainingthe expandable balloon. In some embodiments, the conductive elastomermay take the form of a web or a net. In some embodiments it need notnecessarily embrace the full circumference of the operative element;embracing a representative partial expanse of an expandablecircumference can be sufficient to derive circumferential sizinginformation. In addition to positioning the conductive elastomer on asurface exterior to an expanding portion of the operative element, insome embodiment, a conductive elastomer may be adhered to an innersurface of an expanding member such as a balloon. The only requirementin serving the object of the present invention is that the degree oflinear stretch of the elastomer relates to the circumference of theoperative element. Some embodiments of the invention may include both ofthe basic forms of resistivity sizing features as described herein,i.e., some embodiments may include circuits that include sections ofsize-sensing conductive elastomer, as described, as well as size-sensingcircuits associated with the mutual area of overlap of overlappingexpandable electrode supports. In such embodiments, algorithms may beemployed to integrate separate sources of sizing information to yield anoptimal result.

The provision of one or more bands of conductive elastomer 180 toprovide information that relates directly to the circumference of anoperative element is broadly applicable to many ablational operativeelements that expand to make therapeutic contact with a body lumen. U.S.Pat. No. 7,150,745 of Stern et al. (incorporated herein, in itsentirety), for example depicts embodiments of operative elements inFIGS. 2-4; further embodiments are shown in FIGS. 8-18. Each of theseembodiments can be fitted with one or more conductive elastomeric bands180, and thus are included as embodiments of the present invention.

Various of the ablational system and method embodiments provided in U.S.Pat. No. 7,150,745 of Stern also include an overlapping ablationalenergy delivery element support in which a region where the longitudinaledges of the support mutually overlap is related to the degree ofcircumferential expansion provided by an expandable mechanism configuredwithin the circumferential space of the support. These embodimentsinclude those depicted in FIGS. 14A and 14B, 15A-15C, 16, and 17 (ofU.S. Pat. No. 7,150,745). FIG. 15C is an embodiment that varies from theothers by having two such regions where longitudinal edges of supportsoverlap. Each of these operative elements can be fitted with electrodesthat provide sizing information as depicted in FIGS. 2A-4B of thepresent disclosure, and thus are included as embodiments of the presentinvention.

U.S. Pat. No. 7,150,745 of Stern et al. (incorporated herein, in itsentirety) further includes description of various configurations ofablational energy delivery elements in the form of electrode arrays thatmay be place on an expandable electrode support (see FIGS. 13a-14d ofU.S. Pat. No. 7,150,745). All of these ablational energy deliveryelements may be included on embodiments of operative elements and theiroverlapping electrode supports as described in this specification andare hereby included as embodiments of the present invention.

Typical embodiments of the device of the present invention includeradiofrequency delivery elements as the means by which to distributeablative energy into targeted luminal tissue. The radiofrequencyelements may be monopolar or biopolar electrodes, an electrode array ofany pattern, or solid-state circuitry. As described above, theseelements may, in some embodiments be arranged directly on an inflatablemember such as a balloon, and in other embodiments be arranged on anelectrode support, which itself is engaged at least partially around aballoon. Although the exemplary embodiments described herein typicallydistribute radiofrequency energy delivered by appropriate means, someembodiments may make use of other forms of ablative energy andappropriate distribution elements, such as microwave energy emanatingfrom an antenna, light energy emanating from photonic elements, thermalenergy transmitted conductively from heated ablational structuresurfaces or as conveyed directly to tissue by heated gas or liquid, or aheat-sink draw of energy, as provided by cryonic cooling of ablationalstructure surfaces, or as applied by direct cold gas or fluid contactwith tissue.

U.S. patent application Ser. No. 12/114,628 of Kelly et al., entitled“Method and apparatus for gastrointestinal tract ablation for treatmentof obesity”, as filed on May 2, 2008 further includes embodiments ofelectrode arrays can effect a fractional ablation (see FIGS. 48A-54B); afractional ablation being one in which a portion of the tissue withinthe target area is ablated and another portion is not significantlyaffected. The result of such partial or fractional ablation is depictedin FIG. 55 of the Kelly application (U.S. Ser. No. 12/114,628). All ofthese ablational energy delivery element arrays are compatible devicesand methods for determining the dimensions of a body lumen site targetedfor ablation as described in the present disclosure, and are herebyincluded as embodiments of the invention described herein.

U.S. Pat. No. 7,150,745 of Stern et al. further includes extensivedescription of a generator as a component of a larger system thatcontrols the operation of an ablational operative element. Moreparticularly the generator controls the delivery of power, such asradiofrequency power, to the operative element, for distributiontherefrom into target tissue. Further factors that participate incontrolling the delivery of energy or power from the operative elementinclude the time-course over which energy is delivered, and thetemperature and impedance of target tissue. A constancy in the rate ofpower delivery is provided by a proportional derivative controller,which increases power level, and thus inherently the voltage level,until power reaches a set target value. In one embodiment, the generatoris adapted to control the amount of energy delivered to the tissue overtime based on the measured diameter of the esophagus as provided byresistivity values from the size-sensing circuits described in thisdisclosure, and as depicted in FIGS. 2A-4B (for operative elements thatinclude overlapping electrode supports), and in FIGS. 6A-6C, foroperative elements that include conductive elastomeric circuits.Further, the generator can be adapted to normalize the density of energydelivered to the tissue over time based on the measured diameter of theesophagus so that equivalent energy densities, such that a predeterminedlevel of energy per unit area of electrode surface area (Joules/cm²) canbe delivered to esophagi of differing diameters. In another embodiment,the generator is adapted to control the amount of power delivered to thetissue over time based on the measured diameter of the esophagus so thatequivalent power densities, such that a predetermined and constant levelof power per unit area of electrode surface area (Watts/cm²) can bedelivered to esophagi of differing diameters.

Embodiments of the present invention include a method for ablatingtissue in a body lumen that normalizes ablational energy per unitsurface area of target tissue, as shown in FIG. 7. The system makes useof size-sensing electrical circuits associated with the operativeelement of an ablative device to deliver information that inform alarger system overseeing the operative element of the size of the lumenabout to receive ablative energy. The target tissue is typicallyabnormal, as for example columnar epithelium characteristic of Barrett'sesophagus. However, the tissue itself may not necessarily be abnormal,as for example, ablation of apparently or presumptively normal tissuemay serve a larger therapeutic purpose such as treating obesity (see,for example, the above-referenced U.S. patent application Ser. No.12/114,628). The ablative method includes inserting an expandableoperative element (with an expandable balloon, for example) anablational energy delivery surface, and size-sensing circuitry with aresistivity that varies according to the circumference of the operativeelement into a lumen where targeted tissue is located, expanding theoperative element to a predetermined pressure so as to contact a targetsite in the lumen, varying the sensing circuitry in accordance with thesize of the operative element, measuring the resistivity of thecircuitry associated with the operative element, relating or determiningthe resistivity to a value for the size (e.g., the circumference) of theoperative element, and delivering an amount of ablational energy toachieve a predetermined level of energy delivery per unit surface areaof abnormal tissue being ablated.

Devices and methods related to the present invention are described indetail in U.S. patent application Ser. No. 11/244,385 of Jackson (US2006/0095032), which specification, as noted above, is incorporated inits entirety into this application. That application describes the useof pressure and mass-flow information related to the influx of anexpansion medium into an expandable balloon to derive sizinginformation. The present application also makes use of pressureinformation in order to allow the balloon to be inflated to apredetermined pressure. The appropriate pressure is one that varies overa range from about 1 psig to 7 psig, in some particular embodiments fromabout 3 psig to 5 psig and in some particular embodiments to a pressureof about 4 psig. This pressure, which may in some embodiments bedetermined on a case-by-case basis, but is more typically derived fromgeneral knowledge and experience with the target site. One of thefactors underlying the rationale for the appropriate pressure includesthe intention to effect a coaptive ablation, one in which the flow ofblood into vessels of the region, capillaries in particular, is stoppedby the local application of pressure from the expanded operativeelement, as described in U.S. patent application Ser. No. 11/244,385.Another aspect of the rationale for determining a target pressure towhich balloon should be appropriately inflated relates to the complianceof the targeted lumen, i.e., the degree of change in circumference perunit outwardly applied pressure from within the lumen. These aspects ofrationale thus underlie the step of the presently described method inwhich the balloon is inflated to a predetermined pressure, typicallyabout 4 psig. In other embodiments of the invention that could beapplied to other target sites, or to further another therapeuticobjective, other pressures may be appropriately applied, and thus theuse any appropriate pressure is included as an embodiment of the presentinvention.

Various terms have been used in the description to convey anunderstanding of the invention; it will be understood that the meaningof these various terms extends to common linguistic or grammaticalvariations or forms thereof. Terminology that is introduced at a laterdate that may be reasonably understood as a derivative of a contemporaryterm or designating of a subset of objects embraced by a contemporaryterm will be understood as having been described by the now contemporaryterminology. While some theoretical considerations have been advanced infurtherance of providing an understanding of the invention the claims tothe invention are not bound by such theory. For example, the level ofpressure appropriate for inflating the balloon prior to the delivery ofablational energy is related by theory to the pressure in capillaries ofthe ablation site in order that a coaptive ablation may be effected.Moreover, any one or more features of any embodiment of the inventioncan be combined with any one or more other features of any otherembodiment of the invention, without departing from the scope of theinvention. Further, it should be understood that while these inventivemethods and devices have been described as providing therapeutic benefitto the esophagus by way of example, such devices and embodiments mayalso have therapeutic application in other lumen or cavity sites withinthe body. Still further, it should be understood that the invention isnot limited to the embodiments that have been set forth for purposes ofexemplification, but is to be defined only by a fair reading of claimsthat are appended to the patent application, including the full range ofequivalency to which each element thereof is entitled.

The invention claimed is:
 1. A device for treating a body lumencomprising: an expandable operative element including an inflatableballoon and an ablation energy delivery element support arranged aroundan exterior of the inflatable balloon; and a sensing circuitry mountedto the support, wherein an inductance of the sensing circuitry variesaccording to a relative position between a first sensing element on afirst surface of the ablation energy delivery element support and atleast one of a set of second sensing elements on a second surface of theablation energy delivery element support opposite the first surface,wherein the first sensing element contacts at least one sensing elementof the set of second sensing elements.
 2. The device of claim 1, whereinthe expendable operative element further includes an ablation energydelivery element.
 3. The device of claim 2, wherein the ablation energydelivery element includes any of a radio frequency electrode, a radiofrequency electrode array, or solid-state circuitry.
 4. The device ofclaim 1, wherein the sensing circuitry comprises a portion of a band ofconductive elastomer wrapped around the operative element such that whenthe inflatable balloon is contracted a length of the band of conductiveelastomer is also contracted, and when the inflatable balloon isexpanded, the length of the band of conductive elastomer is stretched.5. The device of claim 1, wherein the ablation energy delivery elementsupport comprises a longitudinal first edge and a longitudinal secondedge that overlap each other to form an area of mutual overlap.
 6. Thedevice of claim 5, wherein the ablation energy delivery element supportis circumferentially expandable by the inflatable balloon such that thearea of mutual overlap is inversely related to an amount of expansion ofthe inflatable balloon.
 7. The device of claim 5, wherein the sensingcircuitry comprises the first sensing element on the first edge and theat least one of the second set of sensing elements on the second edge ofthe ablation energy delivery element support in the area of mutualoverlap, the first sensing element and the at least one of the secondset of sensing elements configured to connect across the area of mutualoverlap to form a circuit with a particular inductance, the firstsensing element and the at least one of the second set of sensingelements further configured such that a connection formed betweensensing elements varies according to an amount of mutual overlap of thetwo edges.
 8. The device of claim 7, wherein the second set of sensingelements comprises a plurality of spaced-apart sensing elements, andwherein the first edge includes the first sensing element and the secondedge includes the plurality of spaced-apart sensing elements, the atleast one of the second set of sensing elements comprising a particularsensing element among the plurality of spaced-apart sensing elements onthe second edge that connects to the first sensing element on the firstedge varying according to the amount of mutual overlap of the two edges,the inductance of the circuit formed varying according to the particularsensing element on the second edge that is included in the circuit. 9.The device of claim 7, wherein the second set of sensing elementscomprises a plurality of closely-spaced sensing elements, and whereinthe first edge includes the first sensing element and the second edgeincludes the plurality of closely-spaced sensing elements, the sensingelements of the edges configured such that the first sensing element onthe first edge connects with one of the plurality of closely-spacedsensing elements on the second edge or with a pair of adjacent sensingelements on the second edge, the one of the plurality of closely-spacedsensing elements or the pair including the at least one of the secondset of sensing elements and the inductance of the circuit formed varyingaccording to which of the one of the plurality of closely-spaced sensingelements or which of the pair of adjacent sensing elements on the secondedge is included in the circuit.
 10. The device of claim 7, wherein thefirst edge includes a single sensing element and the second edgeincludes an elongated sensing element, the elements configured such thatthe single element on the first edge forms a circuit by connecting withthe elongated sensing element on the second edge at a point that variesalong the length of the elongated sensing element thereby creating acircuit of varying length, the inductance of the circuit formed varyingaccording to the length of the enlongated sensing element on the secondedge that is included in the circuit.
 11. The device of claim 1, whereinthe ablation energy delivery element support is furled around theinflatable balloon in a deployable configuration.
 12. The device ofclaim 1, wherein the expandable operative element is configured fordelivery of energy to tissue at a target tissue area.